A new bridge linking north and south Wales is opening after more than two-and-a-half years of work.
The structure over the River Dyfi in Powys cost £46m and replaces an old stone bridge often closed by flooding, sending drivers on a 12-mile diversion.
A haulage company whose lorries pass Machynlleth 40 times a day said it solved one of two bottlenecks it faces in Wales.
"With those sorted would make our lives easier," Scott Mansel Davies said.
Scott Mansel Davies' company MDS Distribution, whose tankers collect milk across Wales, said the Dyfi bridge and the Brynglas tunnels on the M4 in Newport make drivers' lives difficult.
The tunnels in have previously been criticised as the most-congested stretch of inner city motorway in the UK away from the M25, although works have since taken place to try to improve the road.
"Machynlleth has been a bottleneck over the years and it's probably one of two bottlenecks on the roads of Wales. The other one would have to be the Brynglas tunnels on the M4 corridor.
"With those two bottlenecks sorted it would make our lives easier as a haulier. One is sorted now, let's cross our fingers for Brynglas."
He said the diversion, which happens regularly with heavy rain, was a "big headache".
"We've had issues in the planning office with having to rearrange work and redivert drivers.
"The drivers also have the issue of going around Dinas Mawddwy, a far more challenging road and an additional 10 miles and additional 30 minutes out of their scheduling. Which as you can imagine, costs a lot of money but also causes a big headache."
The new road is 1.2km (0.7 miles) and includes a 725m (2,378ft) viaduct which sits nine metres above the River Dyfi floodplain.
New flood prevention measures have also been built to protect the Dyfi Eco Park and a road leading to Machynlleth town centre that passes under a railway line, with emergency surface water pumps installed.
In February last year, the Welsh government said all future road projects must pass strict criteria which means they must not:
increase carbon emissions
increase the number of cars on the road
lead to higher speeds and higher emissions
negatively affect the environment
While the Dyfi bridge project meets those requirements, work began in spring 2021 before the review panel was appointed and does not come as a result of the roads review.
Lee Waters, the Welsh government deputy minister with responsibility for transport, will formally open the new bridge on Friday.
"Our roads policy statement published last year makes clear that we will continue to invest in new and existing roads, but to qualify for future funding the focus must be on minimising carbon emissions, not increasing capacity; not increasing emissions through higher vehicle speeds, and not adversely affecting ecologically valuable sites."
Machynlleth mayor Jeremy Paige said it had been a long wait.
"I think I represent a lot of people when I say we're so pleased that we're getting to a situation where it's going to be open and available to all and the disruption from flooding is removed from this town," he said.
"If you've got children that want to come to school or you need to get to work, it's massively disruptive."
Michael Williams, who has represented Machynlleth on Powys Council since 1980 and has been a town councillor since 1974, said he remembered discussions about a replacement bridge beginning decades ago.
"I didn't think that I would ever see a new bridge because of cost," he said.
"It will encourage people to come into the area for holidays and people won't have to worry about huge delays when the road is flooded."
What is the history of the Dyfi bridge?
The old Dyfi bridge was built in 1805, and according to Mr Williams, the history books say it cost £400 - with the counties of Montgomeryshire and Meirionnydd contributing half each.
"The current bridge was built the year of (the Battle of) Trafalgar, in 1805," he said.
"And I'm pretty sure there weren't many articulated lorries in 1805."
He said the bridge would have been built with the workmen's own hands.
"The workmanship is just tremendous, that the bridge has lasted so long, and to be now holding traffic including articulated lorries on a structure that was built in 1805," he said.
"I have nothing but the greatest admiration for them. And they would have built it physically with their own hands, they wouldn't have had all the mechanical aids.
"So we've really got to appreciate the workmanship of the older generations."